Solar cells that directly convert solar energy to electrical energy have been the subject of rapidly increasing expectations in recent years as next-generation energy sources from the global environmental viewpoint. Solar cells come in a wide variety of types including those that use compound semiconductors or organic materials. Currently, the mainstream solar cells are those which use silicon crystals.
Solar cells that are currently produced and sold in the largest quantity are those which have electrodes formed on a front surface, which is a surface on which the sunlight is incident, and electrodes formed on a back surface opposite the front surface.
However, forming electrodes on the front surface decreases the amount of incident sunlight by an amount corresponding to the area occupied by the electrodes that reflect and absorb the sunlight. Accordingly, development of solar cells in which electrodes are formed on back surfaces is in progress (for example, refer to Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2009-524916 (PTL 1)).
FIG. 21 is a schematic cross-sectional view of an amorphous/crystalline silicon heterojunction device described in PTL 1. As illustrated in FIG. 21, in the amorphous/crystalline silicon heterojunction device described in PTL 1, an intrinsic hydrogenated amorphous silicon transition layer 102 is formed on a back surface of a crystalline silicon wafer 101, an n-doped region 103 and a p-doped region 104 of hydrogenated amorphous silicon are formed on the intrinsic hydrogenated amorphous silicon transition layer 102, electrodes 105 are formed on the n-doped region 103 and the p-doped region 104, and an insulating reflection layer 106 is formed between the electrodes 105.
In the amorphous/crystalline silicon heterojunction device described in PTL 1 illustrated in FIG. 21, the n-doped region 103 and the p-doped region 104 are formed by lithography and/or a shadow masking process (for example, refer to paragraph 0020 and the like of PTL 1).